|
Molybdenum is a chemical element in the periodic table. Its symbol is Mo and its atomic number 42.
Biological role
Molybdenum has been found to have a role in the biology of all classes of organisms. It is found in two groups of enzymes, the nitrogenases and the molybdopterins.
The nitrogenases are found in bacteria, and are involved in the pathways of nitrogen fixation. The bacteria may be found inside plants. The molybdenum atom is present in a cluster(see cluster chemistry), which includes iron and sulfur atoms. The name molybdopterin is misleading as the group of enzymes includes tungsten-containing enzymes, and the word molybdopterin does not actually refer to the metal atom. The group may also be referred to as the mononuclear molybdenum enzymes as the metal atom is not present in a cluster. This group of enzymes is involved in a variety of processes, as part of the global sulfur, nitrogen and carbon cycles, and generally involve an oxygen atom transfer as part of the process.
There is a trace requirement for molybdenum in plants, and soils can be barren due to molybdenum deficiencies. Plants and animals generally have molybdenum present in amounts of a few parts per million. In animals molybdenum is a cofactor of the enzyme xanthine oxidase which is involved in the pathways of purine degradation and formation of uric acid. In some animals, adding a small amount of dietary molybdenum enhances growth.
Francis Crick suggested that since molybdenum is an essential trace element that plays an important role in many enzymatic reactions, despite being less abundant than the more common elements, such as chromium and nickel, that perhaps this fact is indictative of Panspermia. Crick theorized that if it could be shown that the elements represented in terrestrial living organisms corelate closely with those that are abundant in some class of star - molybdenum stars, for example, that this would provide evidence of such Directed Panspermia.
Toxicity in animals
In ruminants, the molybdenum toxicity occurs if the animals are let to graze on soil rich in molybdenum, but deficient in copper. The molybdenum causes excretion of copper reserves from the animal and cause copper deficiency. In young calves, the molybdenum toxicity is manifested as teart or shooting diarrhoea, where the dung is watery, full of air bubbles and with a fetid odor. In pig and sheep, molybdenum toxicity combined with copper deficiency can lead to a condition called sway back or paralysis of hind quarters. In black coated animals, the toxicity of this metal is characterized by depigmentation of the skin surrounding the eyes, which is often referred to as spectacled eyes
|
